In recent years, semiconductor chips have been remarkably evolved to thin-filmed and smaller-sized chips. In particular, in the case of IC cards, such as memory cards and smart cards, in which semiconductor IC chips are embedded, the semiconductor chips each require a thickness of 100 μm or less. As those demands will increase in the future, it is assumed that the needs for the above thin-filmed and small-sized chips increase much more.
Those semiconductor chips can be obtained by processing a semiconductor wafer into a thin film having a predetermined thickness by a back-grinding process, etching process, or the like, and then supporting and fixing the semiconductor wafer with a dicing tape or the like, followed by chipping with a dicing process. Subsequently, when the dicing tape has a removable adhesive layer of a radiation-curable type, the chips are transferred to a pick-up process after irradiating with radiation, such as ultraviolet rays or electron beams, and then mounted on a lead frame or the like after passing through pick-up and die-bonding processes.
Of a series of the above processes, for the dicing process, a general method is a blade-cutting system involving cutting a semiconductor wafer with a dicing blade while supporting and fixing the semiconductor wafer with a dicing tape. In this case, however, the blade is set to a rotational frequency of several tens of thousands rpm in approximate and thus the blade will have frictional heat by receiving considerable cutting resistance. In some cases, the blade may have an increased surface temperature of about 100° C. In general, when the wafer is fully cut off, depending on circumstances, the base film of the tape can be also cut off with a blade and thus a part of the base film can be molten by heat of the blade. As a result, there is a case that filamentous dicing waste is generated and scooped out on the surface pattern of the wafer. When, for example, the waste adheres on an electrode pad, there is a possibility of leading to trouble in subsequent wire-bonding. In the case of a thick wafer as before, even if filamentous dicing waste has been generated, the degree of the generation is to the extent that it remains on the chip side. For this reason, there was no fear of leading to trouble in wire bonding as mentioned above. However, the formation of a wafer into a thin film in recent years tends to allow filamentous dicing waste to be generated even on the surface of the wafer, causing the trouble as mentioned above to be more serious.
For the method of solving such a trouble, a tape for processing a wafer in which a removable adhesive agent is applied on a cross-linked base film has been proposed (see, for example, JP-A-5-211234 (“JP-A” means unexamined published Japanese patent application)). In addition, there is proposed a method involving forming a viscoelastic layer hardened by an energy beam on a base film and confining the cut in an adhesive sheet for dicing by dicing up to the viscoelastic layer but not to the base film (see, for example, JP-A-2003-7646).
However, in the former, the base film is cut with a blade under a high-temperature condition, and thus it is not necessarily sufficient when the thickness of the wafer is in the range of 100 μm or less. In the latter, on the other hand, the blade does not cut the base film, so that no incident such as the generation of filamentous dicing waste by fusion of the tape due to the heat of the blade as described above occurs. In this case, however, the viscoelastic layer is very thick as much as 300 μm in maximum thickness and is formed as a hard layer hardened by an energy beam. Thus, fine powdery cutting waste may be undesirably caused from the viscoelastic layer when the blade cuts the viscoelastic layer at the time of dicing. In addition, if the powdery cutting waste has adhered on an electrode pad having a patterned surface, there is a problem in that the possibility of leading to poor wire-bonding may occur and simultaneously the remarkable abrasion of the blade may occur owing to cut of the thick, hardened viscoelastic layer to lead to a decrease in lifetime of the blade.